efifb: BGRT: Add nobgrt option

In some setups restoring the BGRT logo is undesirable, allow passing
video=efifb:nobgrt on the kernel commandline to disable it.
Reported-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/efifb.c

@@ -42,6 +42,7 @@ struct bmp_dib_header {
 	u32 colors_important;
 } __packed;
 
+static bool use_bgrt = true;
 static bool request_mem_succeeded = false;
 static u64 mem_flags = EFI_MEMORY_WC | EFI_MEMORY_UC;
 
@@ -160,6 +161,9 @@ static void efifb_show_boot_graphics(struct fb_info *info)
 	void *bgrt_image = NULL;
 	u8 *dst = info->screen_base;
 
+	if (!use_bgrt)
+		return;
+
 	if (!bgrt_tab.image_address) {
 		pr_info("efifb: No BGRT, not showing boot graphics\n");
 		return;
@@ -290,6 +294,8 @@ static int efifb_setup(char *options)
 				screen_info.lfb_width = simple_strtoul(this_opt+6, NULL, 0);
 			else if (!strcmp(this_opt, "nowc"))
 				mem_flags &= ~EFI_MEMORY_WC;
+			else if (!strcmp(this_opt, "nobgrt"))
+				use_bgrt = false;
 		}
 	}